Ophthalmic examinations are commonly made for the early diagnosis of various diseases that come before lifestyle-related diseases and causes of blindness. Since a medical examination or the like is required to find a disease in a whole eye portion, an examination using an image over a broad range of the eye portion (to be referred to as a fundus image hereinafter) is indispensable. The fundus image is captured using a fundus camera or SLO (Scanning Laser Opthalmoscope). On the other hand, a tomography apparatus for an eye portion such as an OCT (Optical Coherence Tomography) is expected to effectively give more adequate diagnoses of diseases since it allows to three-dimensionally observe the state of the interior of retina layers.
FIG. 5A is a pattern diagram of a macula tomogram of a retina captured by the OCT. A tomogram of an eye portion by the OCT is three-dimensionally obtained. In FIG. 5A, reference symbols T1 to Tn denote two-dimensional (2D) cross-sectional images (B-scan images) of a macula portion. Then, reference numeral 1 denotes an inner limiting membrane; 2, a boundary between a nerve fiber layer and its underlying layer (to be referred to as a nerve fiber layer boundary 2 hereinafter); and 2′, a nerve fiber layer. Reference numeral 3 denotes a boundary between an inner plexiform layer and its underlying layer (to be referred to as an inner plexiform layer boundary 3 hereinafter); and 4, a boundary between an outer plexiform layer and its underlying layer (to be referred to as an outer plexiform layer boundary 4 hereinafter). Reference numeral 5 denotes a junction between inner and outer photoreceptor segments; and 6, a retinal pigment epithelium boundary. For example, when such tomogram is input, if the thickness of the nerve fiber layer 2′ (T1 in FIG. 5A) can be measured, a degree of progress of a disease such as glaucoma and a recovery level after a medical treatment can be quantitatively diagnosed. In order to quantitatively measure the thicknesses of these layers, a technique for detecting the boundaries of respective layers of a retina from a tomogram using a computer and measuring the thicknesses of the respective layers is disclosed (see Japanese Patent Laid-Open No. 2008-073099).
On the other hand, in an OCT tomogram, when measurement light is strongly reflected or absorbed by an object, an artifact caused by attenuation or omission of signals is often generated behind the object. Note that the object includes a blood vessel (blood) and exudate. By contrast, a technique which extracts a blood vessel region from a surface image of an eye fundus, back-projects the blood vessel region onto the OCT tomogram, and interpolates layer boundaries in the vicinity of the back-projection region, so as to estimate the layer boundaries in an artifact region caused by the blood vessel has been proposed (see Japanese Patent Laid-Open No. 2007-325831).
On the other hand, it is demanded for an examination using the OCT to detect a plurality of types of ophthalmic diseases such as glaucoma and age-related macular degeneration. Then, since layers of interest in the tomogram are different according to the presence/absence of a disease and the types of diseases, it is demanded to detect layers according to the state of a retina.